Solid materials with a quantity of water and aqueous fluids have long found utility in numerous arts. Both natural and synthetic materials have been developed which will absorb various quantities of aqueous materials.
One of the earliest of such materials was obtained from the marine animal, the sponge. Natural sponges were used in ancient Greece and Rome to apply paint, as mops and by soldiers as substitutes for drinking vessels. Natural sponges absorb considerable amounts of aqueous fluids and, as such, are useful in medicine for absorbing blood and other body fluids, and in industry wherever absorbent material is needed.
However, natural sponges have today been largely replaced by synthetic "sponges". Advantages of synthetic sponges are their more constant supply and their being available in any size or shape desired. Synthetic sponges can be made from a variety of polymers including vinyls, viscose, cellulose, rubber, polyurethane and so forth. Many of the materials themselves are not inherently water absorbent per se and their water holding capacity is a function of the sponge-like physical structure or by use of some absorbing adjunct.
So-called sponge rubber may be made either from dry rubber or from latex. Blowing produces one type of sponge rubber from dry rubber. During vulcanization, the chemicals that have been added turn to gas and "blow" tiny bubbles of air in the rubber compound. When the rubber gels, or sets, in the mold, the bubbles are trapped in it. Blown sponge rubber may be either hard or soft.
Foam rubber is a type of sponge rubber made by whipping air into latex, much as a cook whips air into egg whites. Vulcanization takes place after the foam gels in a mold. Foam rubber has millions of tiny cells filled with air. Some types may be nine-tenths air and only one-tenth rubber. Foam rubber is used for upholstery and foam strips for surgical use. Thus both "sponge rubber" and "foam rubber" are closed cell foams wherein closed voids or cells provide reservoir spaces for liquids.
Polyurethane foams are prepared by reacting a polyisocyanate with a poly-hydroxy compound in the presence of a small amount of water as a "blowing agent". The water reacts with isocyanate groups producing carbon dioxide gas which forms the cells or trapped bubbles when the polyurethane sets.
There has long been interest in producing more highly absorbent materials particularly for use in such products as sanitary napkins, diapers, disposable dust cloths, etc. Many of the prior art materials used to form these products have been non-woven fabrics, papers, pulps, spongy urethane resins, natural sponges and the like. However, these materials exhibit relatively low water absorbency, thus failing to satisfy the need for a low volume, high water absorbent material. Substitutes for these materials such as cross-linked polyethylene oxides, cross-linked polyvinyl alcohols and hydrolyzed products of starch-polyacrylonitrile-grafted polymer have recently appeared on the market. While these products do show increased water absorbency, they also suffer from significant disadvantages in that their water absorbency is still not sufficiently high to justify the costs and the difficulties of production. In addition, some of these materials create disposal problems because they are not biologically degradable. Thus, in the prior art, various proposals to increase the water absorbency and holding capacity for synthetic foams have been advanced.
U.S. Pat. No. 4,104,435 relates to a synthetic sponge comprising a foamed resilient material with a network of fibrous material containing therein.
U.S. Pat. No. 4,717,738 discloses a polyurethane resin based on a hydroxyl containing polymer polyol and a process for making the same.
U.S. Pat. No. 4,725,629 discloses a super absorbent polyurethane foam based on an interconnecting polymer network of a cross-linked polyurethane and a cross-linked addition polymer containing a plurality of chain segments made up of functional groups containing repeating units which may be the same or different.
A biodegradable, high water absorbent polymer has been disclosed in U.S. Pat. No. 4,076,663. While the resins of this patent do show increased water absorbency, their use has been limited to mixing them with sanitary napkins, diapers and other such products wherein the resins are used in their particulate or powder form. Thus, this process fails to disclose the combination of this water absorbent resin with a means for using these polymers within a confined structure or for use with other polymers within a foamed structure, thus retaining the absorbency of the water absorbent material within the confines of a conventional foamed structure.
U.S. Pat. Nos. 4,454,268; 4,337,181 and 4,133,784 disclose various types of films which contain water absorbent polymers. While these patents disclose starch-based, water absorbent polymers prepared from a combination of starch and ethylene acrylic acid copolymers, they fail to disclose the particular type of water absorbent polymer disclosed herein or the mixture of a water absorbent polymer with a conventional polymer which is subsequently foamed to form a foam which exhibits high water absorbency while retaining the characteristics of the polymer which form the polymer foam.
U.S. Pat. No. 3,669,103 discloses water swellable, water insoluble polymeric sorbents for the absorption of aqueous fluids wherein said polymeric sorbents are lightly cross-linked polymers. This patent also discloses the use of a water insoluble polyurethane foam as a support for the polymeric absorbent.
U.S. Pat. No. 4,464,428, describes a closed cell foam of a cross-linked plastic material (such as polyolefin) having a plurality of internal canals which are filled with particulate material, fiber bundles and so forth.
U.S. Pat. No. 4,394,930, relates to an absorbent foam product by reacting under foaming conditions a solids, water insoluble, water-swellable polymer (such as a polyacrylate), a solid blowing agent and a liquid polyhydroxy compound.
U.S. Pat. No. 3,900,030 and U.S. Pat. No. 4,239,043 each describe a means for increasing the absorbency of polyurethane foam catamenial devices. The former suggests using a flexible open-celled foam in which a finely divided, water-swellable polymer is uniformly dispersed and the latter suggest improving foam absorbency by placing on the foam surface 5 to 35%, by weight of cellulose fibers.
Japanese published application Ser. No. 55-168,104 (1982) discloses that loss of water absorbing and water stopping properties of a polyurethane foam can be minimized if the closed-cell polyurethane foam contains both independent air bubbles as well as water-absorbing resin particles of a specific size range. Water absorbing resins are disclosed to include polymeric electrolyte prepared by grafting an acrylic acid type monomer onto starch, acrylate polymer or copolymer hydrolysates, cross-linked sodium polyacrylate and so forth.
U.S. Pat. No. 4,731,391, discloses a method of preparing a superabsorbent polyurethane foam wherein polyurethane foam precursors are mixed and reacted under foaming and free radical conditions with an ethylenically unsaturated compound such as an acrylate, methacrylate or acryamide.
Japanese published application Ser. No. 57-92,032 (1982) disclosed a polyurethane foam that contains a water absorbent polymer wherein the percentage of the air bubble formation is in the range of 1 to 60 percent, wherein the diameter of the cells is in the range of 200 to 400 microns and wherein the size of the water absorbent resin is in the range from about 200 to 400 microns.
Thus, the art has long sought a synthetic material which will absorb and hold large quantities of water. It is therefore one object of the present invention to provide a synthetic structure which will absorb and hold large quantities of aqueous liquids. It is another object of this invention to prepare polymer foams which are highly water absorbent and which have the ability to retain and hold a high water content.
It is a further object of this invention to prepare foamed polyurethane polymers containing highly water absorbent resin.
It is still a further object of this invention to provide water absorbent foams which can be useful for the absorbence of fluids while retaining their basic shape.
These and other objects, as well as the scope, nature, and utilization of this invention, will be apparent from the following description.